The present invention relates to an image forming apparatus applicable as, for example, a color printer, a color copying machine, a color facsimile, and the like, and in particular, to a color electrophotographic apparatus forming a color image by using electrophotography and to an image forming unit used therefor.
FIG. 7 is a cross-sectional view showing a conventional image forming unit taken along a plane through its center. The image forming unit shown in FIG. 7 includes a photosensitive member, a charger, a developing means, a cleaning means, a box, and the like.
In FIG. 7, numeral 100 denotes an image forming unit, which is formed integrally as one unit including a photosensitive member 110 and process elements provided therearound. Each element includes the following parts.
Numeral 121 denotes a charger for homogeneously charging the photosensitive member 110, and 123 denotes a developing means including a developing roller 122. Numeral 125 denotes a toner hopper containing toner 124. The toner 124 is supported on the surface of the developing roller 122 of the photosensitive means 123 and develops the photosensitive member 110. Numeral 126 denotes a cleaning means for removing toner remaining on the surface of the photosensitive member 110, which includes a rubber cleaning blade 127 and a waste toner case 128 for containing waste toner. Numeral 129 denotes an exposure window opening for a laser beam to enter the image forming unit 100.
FIG. 8 is a perspective view showing a drive side flange of the photosensitive member with which a gear for driving to rotate the photosensitive member is integrated.
As shown in FIG. 8, at one end of the photosensitive member 110, the drive side flange 111 is fixed. The drive side flange 111 is formed integrally into one unit with a gear portion 111A receiving a rotation driving force from the apparatus main body. On the other end of the photosensitive member 110 opposing to the drive side flange 111, a non-drive side flange (not shown) is fixed. The photosensitive member 110 is held in a box 130 by a photosensitive member axis 112 supporting while rotating each flange attached to the photosensitive member 110 at the axis of the photosensitive member 110. Furthermore, the photosensitive member 110 is positioned at the image forming position of the apparatus main body at both ends of the photosensitive member axis 112. Moreover, numeral 131 denotes washers provided at both ends of the photosensitive member 112 so that the photosensitive member axis 112 is not prevented from dropping from the box 130. Furthermore, at the drive side flange 111, a metal plate 113 is provided in contact with both the photosensitive member 110 and the photosensitive member axis 112 so that the photosensitive member 110 conducts to the apparatus main body.
Also in a color printer, a color copying machine, a color facsimile, and the like, similar to monochrome ones, there is a demand towards a high quality image, small size and low cost by producing the image forming apparatus by forming each image forming member as one unit, thus facilitating the handling. Above all, in order to improve the image quality, it is required to improve the positioning accuracy and the rotating accuracy of the photosensitive member of each image forming unit in the photosensitive member at the image forming position.
It is an object of the present invention to provide an image forming unit having a simple structure, capable of reduction in size and weight, and realizing a high quality image, and an image forming apparatus capable of improving the positioning and the rotating accuracy of the photosensitive member at the image forming position by using the image forming unit.
In order to attain the above-mentioned object, an image forming unit according to the present invention includes a photosensitive member on the surface of which an electrostatic latent image is formed; a charger for charging the photosensitive member; a developing means for developing the electrostatic latent image into a visible image; and a box for supporting the photosensitive member, the charger and the developing means; and wherein a first flange that is integrally formed into one unit including a positioning part with respect to the image forming apparatus main body for positioning the photosensitive member at the image forming position of the image forming apparatus main body and a rotation engaging portion for receiving a rotation driving force from the image forming apparatus main body is attached to at least one end of the photosensitive member. According to this configuration of the image forming unit, it is possible to lighten and simplify the photosensitive member, to support the photosensitive member axis by the image forming apparatus main body, and to rotate the photosensitive member easily by the axis itself. Therefore, positioning accuracy and rotating accuracy of the photosensitive member are improved. As a result, it is possible to align colors accurately, which is important when forming a color image. Thus, a high quality image can be obtained.
Furthermore, it is preferable in the image forming unit according to the present invention that the positioning part is a hole or a concave portion provided concentrically with respect to the photosensitive member axis. According to such a preferable configuration, it is possible to guide the positioning means of the image forming apparatus main body to the positioning part easily and to carry out the positioning by the photosensitive member axis. As a result, it is possible to reduce rocking in rotation of the photosensitive member at the time of rotation driving, and thus a high quality image can be obtained.
Furthermore, it is preferable in the image forming unit according to the present invention that a second flange that is integrally formed into one unit including a positioning part for positioning with respect to the image forming apparatus main body is attached to the other end of the photosensitive member opposing the first flange. According to such a preferable configuration, it is possible to simplify the structure of the photosensitive member. Furthermore, since the positioning parts of both of the first flange and the second flange with respect to the image forming apparatus main body are provided in the flange main body, the photosensitive member can be positioned at the image forming position of the image forming apparatus main body at high accuracy. Furthermore, in this case, it is preferable that the second flange is provided with a rotation engaging portion for conveying the rotation driving force from the image forming apparatus main body. According to such a preferable configuration, since it is possible to convey the rotation driving force of the photosensitive member to the positioning means of the image forming apparatus main body that engages the second flange, the positioning means is allowed to rotate together with the second flange so as to inhibit the sliding between the rotation engaging portion of the second flange and the positioning means. As a result, it is possible to prevent the positioning part of the second flange from being deformed and, at the same time, to prevent mislocation in positioning the photosensitive member, and a high quality image can be obtained. Furthermore, in this case, it is preferable that both ends of the photosensitive member are rotatably bearing supported by the box in the outer circumference of the first and second flanges. According to such a preferable configuration, it is possible to use the side face of the flange effectively. In particular, by positioning the photosensitive member at the axis of the photosensitive member of each flange, the rotation accuracy of the photosensitive member can be increased. Thus, the accuracy in aligning colors can be enhanced, thus to obtain a high quality image. Furthermore, it is preferable in this case that the bearing supporting portions for supporting the first and second flanges formed in the box are formed in approximately U-shaped grooves having a thickness that is larger than an outer diameter of the part of the first and second flanges that is bearing supported. According to such a preferable configuration, it is possible to attach/detach the photosensitive member to/from the box easily.
Furthermore, it is preferable in the image forming unit according to the present invention that at least one of the first flange and the second flange is made of a conductive material. According to such a preferable configuration, conduction to the image forming apparatus main body can be taken simply without using an additional component for conducting to the image forming apparatus main body in the photosensitive member. Furthermore, since there is no load due to the sliding friction of the component for conducting to the image forming apparatus main body, it is possible to enhance the rotation accuracy of the photosensitive member.
Furthermore, it is preferable in the image forming unit according to the present invention that the rotating engaging portion of the first flange is a concave and convex surface formed on one end face of the first flange and the concave and convex surface is located at the outer-most side portion. According to such a preferable configuration, the moving amount of the rotation driving means of the image forming apparatus main body can be reduced, thus to realize the miniaturization of the image forming apparatus main body. Furthermore, in this case, it is preferable that the image forming unit further includes a cover that has substantially the same height as the rotation engaging portion of the first flange and protects the first flange. According to such a preferable configuration, since it is possible to protect the entire part of the flange outer circumference of the bearing supported flange and the rotation engaging portion, it is possible to prevent the positioning part, rotation engaging portion, and bearing supported outer circumference from being damaged due to impact from the outside.
Furthermore, an image forming apparatus according to the present invention includes a plurality of image forming units for different colors having a photosensitive member; an image forming unit conveying means for switching the plurality of image forming units by moving them successively between an image forming position and a waiting position; a positioning means for positioning the photosensitive member at a predetermined image forming position; an exposure means for exposing the photosensitive member; a transfer means for transferring sequentially the toner images of many colors, which are formed on the photosensitive member, to form a toner image in which toner images of a plurality of colors are overlapped on the photosensitive member, and a rotation driving means for driving to rotate the photosensitive member and the transfer means; and wherein an image forming unit according to the present invention is used as the image forming unit. According to this configuration of the image forming apparatus, it is possible to realize an image forming apparatus capable of positioning the photosensitive member at the image forming position of the image forming apparatus main body at high accuracy and at the same time of driving to rotate the photosensitive member at high accuracy. As a result, a high quality image can be obtained.
Furthermore, it is preferable in the image forming apparatus according to the present invention that at least one of the positioning means and the rotation driving means is made of a conductive material that is in contact with and conducts to the first flange or second flange. According to such a preferable configuration, conduction to the photosensitive member can be taken simply and easily without using additional component.
Furthermore, it is preferable in the image forming apparatus according to the present invention that a brake means for providing the photosensitive member with a braking power via the second flange is further included. According to such a preferable configuration, it is possible to suppress the change in rotation of the photosensitive member when the photosensitive member is rotated by the rotation driving force of the developing roller that is in contact with the photosensitive member when the photosensitive member is rotating. Therefore, the rotating accuracy of the photosensitive member can be improved. As a result, a high quality image can be obtained.